The use of Electronic Article Surveillance, Radio Frequency Identification, and electronic security tag technology (hereinafter collectively referred to as ‘RFID’) is becoming increasingly prevalent in manufacturing, inventory control, retail and residential settings. RFID technology provides efficient, instantaneous communication between a reader and an RFID tag without direct line-of-sight scanning, as is commonly required in more conventional automatic identification technologies (e.g., bar-code, optical scanning, etc.). RFID technology involves the transmission of information through radio waves. A typical RFID system includes an RFID tag and an RFID reader/encoder. First used many decades ago in military and espionage applications, RFID technology is now emerging as a valuable tool in commercial and domestic settings. For example, RFID technology is used by manufacturers or retailers to instantaneously track product inventories and thereby adjust to specific inventory needs. Similarly, RFID technology can be used by automobile commuters to pay highway tolls without interrupting their commute, or by pet owners to provide reassurance that pets are readily locatable, regardless of lost collars.
RFID tags typically include an electronic circuit chip and an antenna attached to the circuit chip. The circuit chip and antenna are generally thin, flexible, and mounted to a flexible dielectric substrate. Antennas have numerous configurations and each is structured generally to collect and broadcast electromagnetic energy from a distant reader. RFID chips can be programmed to store a variety of information. For example, RFID chips often include retail product identification such as a product serial number. In other applications, relatively more complex information may be provided such as biometric information on an employee ID badge. Such applications may include “smart cards,” which include an RFID tag or inlay integrated into the card.
RFID tag and reader systems may operate over a wide range of frequencies, including low-frequency (LF) applications, high-frequency (HF) applications, and ultra-high-frequency applications (UHF). LF applications typically operate from 125-148.5 kHz. HF applications typically operate at 13.56 MHz. UHF applications typically operate from 300 MHz to 3 GHz. The “read range” of an RFID tag and reader system is often defined as the distance from which a reader can communicate with a tag. Read ranges can be affected by variety of factors. For example, active RFID tags (as opposed to passive RFID tags) have independent power sources (typically batteries), and have relatively longer read range. However, active RFID tags are more expensive and may be less reliable than passive RFID tags due to the need to replace the battery. In theory, passive RFID tags have an infinite life, but offer shorter read ranges.
Passive LF and HF applications offer very short read ranges, often requiring the RFID tag to be within 1 to 12 inches of a reader for successful communication. Passive UHF applications typically offer longer read ranges, allowing RFID tags to be within 2 to 5 meters or more of a reader for successful communication. However, various environmental factors can detune an RFID tag, thus modifying the operating frequency and potentially affecting the read range of the RFID tag. RFID tags in the presence of metals and liquids may experience detuning due to absorption or parasitic capacitance provided by these materials.
Additionally, due to the high water content of the human body, a user may detune an RFID tag simply by using it. This is especially troublesome for RFID tags (inlays) imbedded within access cards that are held by a user when read by a reader. For example, in certain instances, a user may unknowingly detune an RFID access card by obscuring the card while attempting to hold the card near a reader. In other instances, a user may detune an RFID access card by wearing the card on a lanyard such that the card is adjacent the user's body. Although strategic handling of the access card may reduce the detuning effect (such as handling the card only by its edges or extending the card away from the user's body), these solutions defeat the convenience and speed advantages provided by RFID technology.
As a result, there is a need for an improved RFID tag design that reduces various detuning effects, including that of a user handing an RFID tag in the presence of a reader.